Method and apparatus for speciating hydrocarbons

ABSTRACT

Described herein are a method and apparatus for analyzing a gas sample that is conveyed in a drilling fluid, and a method and apparatus for liberating gases from drilling fluid. The gas sample contains one or more of methane, ethane, propane, and butane; optionally, the gas sample may also contain pentane. The gas sample is first liberated from the drilling fluid, following which it is irradiated with infrared radiation in the near-infrared range. Absorption spectra resulting from absorption of the infrared radiation by the one or more of methane, ethane, propane and butane is simultaneously detected. From the absorption spectra, the composition of the gas sample can be determined. The composition includes a concentration of any one or more of the methane, ethane, propane and butane. Linearity of absorption is increased by using relatively short wavelength infrared radiation centred on, for example, about 1.70 μm, which can increase the accuracy of and reduce the computational intensity of the calculations utilized to determine the composition of the gas sample. Within the near-infrared range, radiation having a wavelength from about 1.55 μm to 1.85 μm can be used. Gases can be liberated from the drilling fluid using a gas trap. The gas trap can be powered using a brushless DC motor, and alternatively or additionally drilling fluid from a sample enclosure of the gas trap can exit via a bubbler enclosure of the gas trap. The brushless DC motor is a relatively efficiency and compact motor that can be used with the gas trap, and is advantageous over convention AC induction and air motor motors. Having drilling fluid exit the sample enclosure through the bubbler enclosure is advantageous in that it helps to make the footprint of the gas trap relatively small.

CROSS REFERENCE TO RELATED APPLICATION

Pursuant to 35 U.S.C. §119(e), this application claims the benefit ofprovisional U.S. Patent Application No. 61/355,951, filed Jun. 17, 2010and entitled “Method and Apparatus for Speciating Hydrocarbons,” whichis hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure is directed at a method and apparatus forspeciating hydrocarbons and at a method and apparatus for liberatinggases from drilling fluid. More particularly, the present disclosure isdirected at a gas analyzer for speciating any one or more of methane,ethane, propane, butane and pentane conveyed in a drilling fluid, and ata gas trap that can be used with the gas analyzer.

BACKGROUND

During oil and gas well drilling, drilling fluid (also known as“drilling mud”) is typically pumped from the surface down the well thatis being drilled. This may be done for multiple reasons. The drillingfluid may, for example, provide cooling, lubrication, and may act as amedium through which communication signals that originate downholepropagate to the surface. When drilling fluid is used in oil and gasdrilling, hydrocarbons from the formation that is being drilled comeinto contact with the drilling fluid and are absorbed by the drillingfluid. The drilling fluid transports these absorbed hydrocarbons to thesurface where they can be separated from the drilling fluid andanalyzed. The hydrocarbons present in the drilling fluid can indicatethe likelihood that the well being drilled will produce significantquantities of oil or gas.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate one or more exemplaryembodiments: FIG. 1 is a block diagram of a drilling site that has on ita gas analyzer according to a first embodiment.

FIG. 2 is a schematic of the gas analyzer of FIG. 1.

FIG. 3 is a block diagram of components disposed on an electronics boardof the gas analyzer of FIG. 1.

FIGS. 4( a) and (b) are perspective and sectional views, respectively,of a hydrocarbon sensor located in the gas analyzer of FIG. 1.

FIGS. 5( a) and (b) are flowcharts describing a method of operating thegas analyzer of FIG. 1, according to a second embodiment.

FIGS. 6( a) to (e) are exemplary absorption spectra for each of methane,ethane, propane, butane and pentane, respectively, measured duringoperation of the gas analyzer of FIG. 1.

FIG. 7 is a perspective view of a gas trap according to a secondembodiment.

FIG. 8 is a front elevation view of the gas trap of FIG. 7.

FIG. 9 is a sectional view of the gas trap of FIG. 7, taken along line9-9 of FIG. 7.

FIG. 10 is a bottom plan view of the gas trap of FIG. 7.

FIG. 11 is a top plan view of the gas trap of FIG. 7.

FIG. 12 is a rear elevation view of the gas trap of FIG. 7.

DETAILED DESCRIPTION

According to a first aspect, there is provided a method for analyzing agas sample conveyed in a drilling fluid. The method includes liberatingthe gas sample from the drilling fluid, wherein the gas sample comprisesone or more of methane, ethane, propane, and butane; irradiating the gassample with infrared radiation spanning a wavelength range comprisingnear-infrared wavelengths; simultaneously detecting absorption spectraassociated with irradiating each of the one or more of methane, ethane,propane, and butane; and determining a composition of the gas samplefrom the absorption spectra, the composition comprising a concentrationof any one or more of the methane, ethane, propane and butane.

The wavelength range can be from about 1.55 μm to about 1.85 μm.

The absorption spectra can be used to determine how much pentane ispresent in the gas sample, and how much carbon dioxide is present in thegas sample.

The butane may include one or both of i-butane and n-butane.

Determining the composition of the gas sample may include determiningthe concentrations of any two or more of the methane, ethane, propaneand butane; any three or more of the methane, ethane, propane andbutane; or the concentrations of each of the methane, ethane, propaneand butane.

A tunable laser diode can be used to emit the infrared radiation.

Liberating the gas sample from the drilling fluid can be performed usinga gas trap, and air may be pumped from an air source into the gas trapto maintain the drilling fluid at a certain height within the gas trap.The gas sample may be heated after it is liberated from the drillingfluid and the air from the air source may be heated prior to beingpumped into the gas trap.

The method may also include pressurizing, in a pressure reservoir, airfrom the air source; and discharging pressurized air from the pressurereservoir into a flowline used to intake the gas sample from the gastrap to clear the flowline.

According to another aspect, there is provided an apparatus foranalyzing a gas sample extracted from a drilling fluid. The apparatusincludes a sample inlet configured to receive the gas sample, whereinthe gas sample comprises one or more of methane, ethane, propane, andbutane; a hydrocarbon sensor comprising a gas cell fluidly coupled tothe sample inlet and configured to contain a portion of the gas sample;an infrared emitter positioned to irradiate the gas cell with infraredradiation spanning a wavelength range comprising near-infraredwavelengths; a detector aligned with a path of the infrared radiation tosimultaneously detect absorption spectra associated with irradiatingeach of the one or more of methane, ethane, propane, and butane withinthe gas cell; a sample outlet fluidly coupled to the gas cell andconfigured to discharge the gas sample; and a processor communicativelycoupled to the detector and to a memory, the memory having statementsand instructions encoded thereon to configure the processor to determinea composition of the gas sample from the absorption spectra, thecomposition comprising a concentration of any one or more of themethane, ethane, propane and butane.

The wavelength range may be from about 1.55 μm to about 1.85 82 m.

The statements and instructions encoded on the memory may furtherconfigure the processor to determine how much pentane is present in thegas sample.

The apparatus may also include a carbon dioxide detector fluidly coupledto the gas cell, and the statements and instructions encoded on thememory may further configure the processor to determine how much carbondioxide is present in the gas sample.

The statements and instructions encoded on the memory may furtherconfigure the processor to determine how much of one or both of n-butaneand i-butane are present in the gas sample.

The statements and instructions encoded on the memory may configure theprocessor to determine the concentrations of any two or more of themethane, ethane, propane and butane; of any three or more of themethane, ethane, propane and butane; or of each of the methane, ethane,propane and butane.

The infrared emitter may be a tunable laser diode.

The apparatus may also include a bubbler pump, a bubbler inlet and abubbler outlet, wherein the bubbler pump is fluidly coupled to thebubbler outlet and to an air source via the bubbler inlet and isconfigured to pump bubbler air out through the bubbler outlet.

The apparatus may also include a gas trap configured to liberate the gassample from the drilling fluid, and having a bubbler air port fluidlycoupled to the bubbler pump via a bubbler air conduit and a gas sampleport fluidly coupled to the sample inlet via a gas sample conduit,wherein the bubbler air pumped from the bubbler pump through the bubblerair conduit and into the bubbler air port maintains the drilling fluidat a certain height within the gas trap and wherein the gas sample isdischarged through the gas sample port and gas sample conduit to thesample inlet.

The apparatus may also include a tubing bundle surrounding the bubblerair and gas sample conduits, the tubing bundle having a heat traceconfigured to heat the bubbler air and gas sample conduits.

The apparatus may also include a sample filter; and valving configurablein measurement, pressurizing and purging states. The valving can fluidlycouple the sample inlet to the hydrocarbon sensor through the samplefilter when in the measurement state, fluidly couple the bubbler pump tothe sample filter such that pressure builds within the sample filterwhen in the pressurizing state, and fluidly couple the bubbler pump tothe sample inlet through the sample filter when in the purging statesuch that pressurized air within the sample filter can be dischargedthrough the sample inlet.

According to another aspect, there is provided an apparatus forliberating gases from drilling fluid. The apparatus includes a sampleenclosure having a liquid inlet and a gas sample outlet; an agitatordisposed within the sample enclosure and configured to agitate drillingfluid located within the sample enclosure to liberate gases entrained inthe drilling fluid so that the gases can exit through the gas sampleoutlet; and a bubbler enclosure, having a bubbler air inlet and abubbler air outlet, and fluidly coupled to the sample enclosure suchthat the sample and bubbler enclosures are equally pressurized so thatsufficiently pressurized bubbler air entering through the bubbler airinlet maintains the drilling fluid in the sample enclosure at a leveldetermined by the location of the bubbler air outlet when the liquidinlet and the bubbler air outlet are both submerged in the drillingfluid, and such that agitated drilling fluid enters the bubblerenclosure from the sample enclosure.

The sample enclosure may be delineated by a sample enclosure wallcomprising a sample enclosure wall portion and a shared wall portion.The bubbler enclosure may be delineated by a bubbler enclosure wallcomprising a bubbler enclosure wall portion and the shared wall portion.The sample enclosure and the bubbler enclosure may be fluidly coupledthrough the shared wall portion.

The shared wall portion can include a liquid port through which theagitated drilling fluid enters the bubbler enclosure from the sampleenclosure and a gas port through which the bubbler air enters the sampleenclosure, and the liquid inlet may be nearer to the liquid port thanthe gas port.

The agitator can include a shaft having a mixing portion shaped tofacilitate agitation of the drilling fluid. A brushless DC motor may berotatably coupled to the shaft.

The brushless DC motor may include a stator; a rotor directly coupled toa shaft extending from the brushless DC motor and rotatable relative tothe stator in order to rotate the shaft, wherein rotation of the shaftresults in the agitation. The bearings may be oversized relative to atypical, pre-assembled off-the-shelf DC motor so as to accommodate thelength of the shaft.

A sealing portion may be disposed around the shaft between the DC motorand the sample enclosure. The sealing portion may have a first sealingelement configured to prevent solid particulates from entering the DCmotor and a second sealing element configured to prevent liquid fromentering the DC motor. The first sealing element may be nearer to thesample enclosure than the second sealing element. The second sealingelement may include two seals.

The apparatus may also include a disc disposed along the shaft toprevent the drilling fluid from entering the DC motor.

The apparatus may also include a gas sample conduit external to the gastrap and fluidly coupled to the gas sample outlet to transport the gassample outside of the gas trap; and a heat trace thermally coupled tothe gas sample conduit. Alternatively or additionally, the apparatus mayalso include a bubbler air conduit external to the gas trap and fluidlycoupled to the bubbler air inlet to transport the pressurized bubblerair from outside of the gas trap to the gas trap; and a heat tracethermally coupled to the bubbler air conduit. The same heat trace may bethermally coupled to both the gas sample and bubbler air conduits.

The apparatus may also include a gas analyzer having a bubbler pumpfluidly coupled to an air source and configured to output pressurizedbubbler air, wherein the bubbler air inlet is fluidly coupled to thebubbler pump to receive the pressurized bubbler air.

According to another aspect, there is provided a method for liberatinggases entrained in a drilling fluid. The method includes submerging aliquid inlet of a sample enclosure and a bubbler air outlet of a bubblerenclosure in the drilling fluid, wherein the sample and bubblerenclosures are fluidly coupled together such that they are equallypressurized and such that the drilling fluid agitated in the sampleenclosure enters the bubbler enclosure; pressurizing the sample andbubbler enclosures using pressurized bubbler air such that the drillingfluid in the sample enclosure is at a level determined by the locationof the bubbler air outlet; and agitating the drilling fluid within asample enclosure to liberate the gases entrained therein.

The sample enclosure may be delineated by a sample enclosure wallcomprising a sample enclosure wall portion and a shared wall portion.The bubbler enclosure may be delineated by a bubbler enclosure wallcomprising a bubbler enclosure wall portion and the shared wall portion,and the sample enclosure and the bubbler enclosure may be fluidlycoupled through the shared wall portion.

The shared wall portion may include a liquid port through which theagitated drilling fluid enters the bubbler enclosure from the sampleenclosure and a gas port through which the bubbler air enters the sampleenclosure, and the liquid inlet may be nearer to the liquid port thanthe gas port.

Agitation may be powered using a brushless DC motor.

The brushless DC motor may include a stator; a rotor directly coupled toa shaft extending from the brushless DC motor and rotatable relative tothe stator in order to rotate the shaft, wherein rotation of the shaftresults in the agitation. The bearings may be oversized relative to atypical off-the-shelf DC motor having a similar power rating so as toaccommodate the length of the shaft.

The method may also include sealing the DC motor using a first sealingelement configured to prevent solid particulates from entering the DCmotor and a second sealing element configured to prevent liquid fromentering the DC motor. The first sealing element may be nearer to thesample enclosure than the second sealing element. The second sealingelement may include two seals.

The method may also include blocking splashing drilling fluid fromentering the DC motor with a disc disposed along the shaft.

Gases liberated from the drilling fluid may be conveyed away from thesample enclosure using a heated gas sample conduit. Additionally oralternatively, the bubbler air may be conveyed to the bubbler enclosureusing a heated bubbler air conduit.

According to another aspect, there is provided an apparatus forliberating gases from drilling fluid. The apparatus includes a sampleenclosure having a liquid inlet and a gas sample outlet; an agitatordisposed within the sample enclosure and configured to agitate drillingfluid located within the sample enclosure to liberate gases entrained inthe drilling fluid so that the gases can exit through the gas sampleoutlet; and a brushless, DC motor rotatably coupled to the agitator topower the agitator.

The apparatus may also include a bubbler enclosure having a bubbler airinlet and a bubbler air outlet, and fluidly coupled to the sampleenclosure such that the sample and bubbler enclosures are equallypressurized so that sufficiently pressurized bubbler air enteringthrough the bubbler air inlet maintains the drilling fluid in the sampleenclosure at a level determined by the location of the bubbler airoutlet when the liquid inlet and the bubbler air outlet are bothsubmerged in the drilling fluid, and such that agitated drilling fluidenters the bubbler enclosure from the sample enclosure.

The sample enclosure may be delineated by a sample enclosure wallcomprising a sample enclosure wall portion and a shared wall portion.The bubbler enclosure may be delineated by a bubbler enclosure wallcomprising a bubbler enclosure wall portion and the shared wall portion,and the sample enclosure and the bubbler enclosure may be fluidlycoupled through the shared wall portion.

The shared wall portion can include a liquid port through which theagitated drilling fluid enters the bubbler enclosure from the sampleenclosure and a gas port through which the bubbler air enters the sampleenclosure. The liquid inlet can be nearer to the liquid port than thegas port.

The agitator may include a shaft having a mixing portion shaped tofacilitate agitation of the drilling fluid, and the brushless DC motormay include a stator; a rotor directly coupled to a shaft extending fromthe brushless DC motor and rotatable relative to the stator in order torotate the shaft, wherein rotation of the shaft results in theagitation. The bearings may be oversized relative to a typicaloff-the-shelf DC motor having a similar power rating so as toaccommodate the length of the shaft.

There may also be a sealing portion disposed around the shaft andbetween the DC motor and the sample enclosure. The sealing portion mayinclude a first sealing element configured to prevent solid particulatesfrom entering the DC motor and a second sealing element configured toprevent liquid from entering the DC motor. The first sealing element canbe nearer to the sample enclosure than the second sealing element. Thesecond sealing element can comprise two seals.

A disc may be disposed along the shaft to prevent the drilling fluidfrom entering the DC motor.

The apparatus may also include a gas sample conduit external to the gastrap and fluidly coupled to the gas sample outlet to transport the gassample outside of the gas trap; and a heat trace thermally coupled tothe gas sample conduit. Additionally or alternatively, the apparatus mayinclude a bubbler air conduit external to the gas trap and fluidlycoupled to the bubbler air inlet to transport the pressurized bubblerair from outside of the gas trap to the gas trap; and a heat tracethermally coupled to the bubbler air conduit. The same heat trace may bethermally coupled to both the gas sample and bubbler air conduits.

According to another aspect, there is provided a method for liberatinggases entrained in a drilling fluid. The method includes submerging aliquid inlet of a sample enclosure in the liquid; and agitating thedrilling fluid within the sample enclosure to liberate the gasesentrained therein by using a brushless DC motor.

The method may also include submerging a bubbler air outlet of a bubblerenclosure in the drilling fluid, and the sample and bubbler enclosuresmay be fluidly coupled together such that they are equally pressurizedand such that the drilling fluid agitated in the sample enclosure entersthe bubbler enclosure. The sample and bubbler enclosures may bepressurized using pressurized bubbler air such that the drilling fluidin the sample enclosure is at a level determined by the location of thebubbler air outlet.

The sample enclosure may be delineated by a sample enclosure wallcomprising a sample enclosure wall portion and a shared wall portion,the bubbler enclosure may be delineated by a bubbler enclosure wallcomprising a bubbler enclosure wall portion and the shared wall portion,and the sample enclosure and the bubbler enclosure may be fluidlycoupled through the shared wall portion.

The shared wall portion can include a liquid port through which theagitated drilling fluid enters the bubbler enclosure from the sampleenclosure and a gas port through which the bubbler air enters the sampleenclosure, and the liquid inlet can be nearer to the liquid port thanthe gas port.

The brushless DC motor may include a stator; a rotor directly coupled toa shaft extending from the brushless DC motor and rotatable relative tothe stator in order to rotate the shaft, wherein rotation of the shaftresults in the agitation. The bearings may be oversized relative to atypical off-the-shelf DC motor having a similar power rating so as toaccommodate the length of the shaft.

The method may also include sealing the DC motor using a sealing portiondisposed around the shaft and between the DC motor and the sampleenclosure. The sealing portion may include a first sealing elementconfigured to prevent solid particulates from entering the DC motor anda second sealing element configured to prevent liquid from entering theDC motor. The first sealing element may be nearer to the sampleenclosure than the second sealing element.

The method may also include blocking splashing drilling fluid fromentering the DC motor with a disc disposed along the shaft.

Gases liberated from the drilling fluid may be conveyed away from thesample enclosure using a heated gas sample conduit. Alternatively oradditionally, bubbler air may be conveyed to the bubbler enclosure usinga heated bubbler air conduit.

The method may also include generating the bubbler air by using a pumplocated within a gas analyzer.

According to another aspect, there is provided a computer readablemedium having encoded therein statements and instructions configured tocause a processor to execute a method as claimed in any of the foregoingaspects.

Directional terms such as “top”, “bottom”, “upwards”, “downwards”,“vertically” and “laterally” are used in the following description forthe purpose of providing relative reference only, and are not intendedto suggest any limitations on how any apparatus is to be positionedduring use, or to be mounted in an assembly or relative to anenvironment.

Hydrocarbon deposits in the form of oil and gas deposits are oftenlocated underground. Wells are typically drilled in order to accessthese underground deposits. FIG. 1 depicts a drilling site 100 on whichan exemplary oil well 106 is being drilled. A drilling rig 104 is usedto rotationally drive a drill string 108 that has on one of its ends adrill bit 112. Rotation of the drill bit 112 through the earth drillsthe well 106. On the surface is a pump 102 that pumps drilling fluiddown through the drill string 108, out through the drill bit 112, and upback to the surface through the annular region between the drill string108 and the interior surface of the well 106; the path the drillingfluid travels from the pump 102 to the surface is indicated by thearrows in FIG. 1. Optionally, located along the drill string 108 and inthe path of the drilling fluid is a measurement-while-drilling (“MWD”)tool 110. The MWD tool 110 measures various downhole parameters, such asthe resistivity of rock surrounding the drill bit 112 and the amount ofgamma radiation encountered. The MWD tool 110 transmits the measuredparameters to the surface by periodically interrupting the flow of thedrilling fluid, which generates pressure signals indicative of themeasured parameters that are transmitted to the surface through thedrilling fluid that is being pumped down the drill string 108.

When the drilling fluid is forced out through the drill bit 112 andupwards through the annular region between the drill string 108 and theinterior surface of the well 106, it comes into contact with the earththat is being drilled. If the earth contains hydrocarbons, a certainamount of these hydrocarbons dissolve into the drilling fluid and areconveyed back to the surface by the drilling fluid. At the surface, thehydrocarbons in the drilling fluid can be liberated from the drillingfluid and analyzed. A geologist can analyze the hydrocarbons to identifywhich hydrocarbons are contained in the drilling fluid and in whatconcentrations to determine the likelihood that the well 106 will be anoil or gas producing well. A higher proportion of “heavy hydrocarbons”(hydrocarbons containing one or two carbons, such as methane and ethane)relative to “light hydrocarbons” (hydrocarbons containing three or morecarbons, such as butane, propane, and pentane) indicates that the well106 is more likely to produce oil than natural gas; analogously, ahigher ratio of light hydrocarbons to heavy hydrocarbons indicates thatthe well 106 is more likely to produce natural gas than oil.

The embodiments herein are directed at a method and apparatus forliberating the hydrocarbons from the drilling fluid and at a method andapparatus for analyzing the hydrocarbons dissolved in the drillingfluid. In particular, the following embodiments describe a gas trap thatcan be used to liberate the hydrocarbons from the drilling fluid in agaseous form, and a gas analyzer that is capable of individuallyspeciating the gaseous hydrocarbons such that the amount of each ofmethane, ethane, propane, and butane can be measured.

Gas Analyzer

Referring again to FIG. 1, a gas analyzer 114 is depicted in which a gassample that is extracted from the drilling fluid is analyzed. Gas isextracted from the drilling fluid using a gas trap 700, as illustratedin FIGS. 1 and 7 to 12 and as discussed in more detail, below.Alternatively, a gas trap such as a Quantitative Gas Measurement (QGM)gas trap can be used. As described in further detail with respect toFIGS. 2 through 6, below, the gas analyzer 114 analyzes the gas sampleand outputs measurement results to a data recording device 116 such asthe Pason Electronic Drilling Recorder™. Optionally, the data recordingdevice 116 takes into account the time lag it takes for the drillingfluid to reach the surface from the drill bit 112. For example, if thedrill bit 112 is at a depth such that the drilling fluid requires fiveseconds to travel from the drill bit 112 to the surface and be analyzed,the data recording device 116 associates the measurement results notwith the time at which the gas analyzer 114 outputs them, but at thistime minus five seconds. The data recording device 116 is communicativevia a network 118 with a data storage device 120 such as the PasonDatahub™. The data storage device 120 records measurement resultstransmitted to it from the data recording device 116 for subsequentaccess by a data access system 122 also in communication with thenetwork 118, such as a personal computer. In addition to recording andstoring data from the gas analyzer 114, the data recording and storagedevices 116, 120 may also record and store data sent from other devices,such as the MWD tool 110 and various surface sensors (not shown).Notably, while in the present embodiment the drill string 108 includesthe MWD tool 110, in alternative embodiments the MWD tool 110 is notpresent.

Referring now to FIG. 2, there is depicted a schematic of the gasanalyzer 114. The gas analyzer includes a hydrocarbon sensor 202 thatperforms measurements on the gas sample and that generates raw data inthe form of absorption spectra that is analyzed during speciation of thehydrocarbons contained in the gas sample. As discussed in more detail inrespect of FIGS. 4( a) and (b), below, the hydrocarbon sensor 202 passeslight of a range of wavelengths through the gas sample. Depending on thecomposition of the gas sample, different amounts of the light atdifferent wavelengths are absorbed, and the absorption spectra that thehydrocarbon sensor 202 measures varies.

Disposed on the hydrocarbon sensor 202 is a carbon dioxide (CO₂) sensor204 that measures the amount of carbon dioxide in the gas sample whilethe hydrocarbons in the gas sample are being measured. A typical carbondioxide sensor 204 is a Dynament™ carbon dioxide sensor, model numberMSH-P/HCO2/5/V/P. The raw data that the hydrocarbon sensor 202 generatesis amplified by a pre-amplifier/detector 206 (hereinafter a “preamp”)that is electrically coupled to an electronics board 200. Theelectronics board 200 analyzes the raw data and outputs an analysis ofwhat types of and how much of each type of hydrocarbon is present in thegas sample. In the present embodiment, the electronics board 200 outputshow much of each of methane, ethane, propane, butane and pentane ispresent in the gas sample. In alternative embodiments, the electronicsboard 200 can also output how much of each of the various isomers ofpentane is present in the gas, how much of each of the various isomersof butane, such as i-butane and n-butane, is present in the gas, or mayonly output how much of a subset of methane, ethane, propane, butane andpentane is present in the gas (e.g.: only methane, ethane, propane andbutane).

Referring now to FIG. 3, there is depicted a block diagram of the preamp206 connected to components that are on the electronics board 200.Measured absorption spectra that the hydrocarbon sensor 202 outputs areamplified by the preamp 206 and sent, in analog form, to ananalog-to-digital converter (ADC) 306. The ADC 306 outputs digitizedabsorption spectra to a digital signal processor (DSP) 300. The DSP 300is communicatively coupled to three types of memory: SDRAM 322, which isvolatile memory used by the DSP 300 to store runtime data while the DSP300 is operating; calibration flash RAM 324, which is non-volatilememory used to store calibration data generated when the gas analyzer114 is run in a calibration mode, as discussed in more detail below; andfirmware flash RAM 326, which is non-volatile memory used to storeinstructions and algorithms that the DSP 300 executes to analyze themeasured absorption spectra and to speciate the hydrocarbons in the gassample.

When analyzing the measured absorption spectra, the DSP 300 compares themeasured absorption spectra with reference spectra stored in thecalibration flash RAM 324. The reference spectra stored in thecalibration flash RAM 324 includes absorption spectra for each of thehydrocarbons to be identified: methane, ethane, butane, propane andpentane. Examples of each of these reference spectra are pictured inFIGS. 6( a) to (e). Based on the degree to which the measured absorptionspectra corresponds with the reference spectra stored in the calibrationflash RAM 324, the DSP 300 speciates the gas sample by determining whatproportion of each of methane, ethane, butane, propane and pentane ispresent in the gas sample. An example of how reference and measuredabsorption spectra are compared in order to result in identification ofconstituents of the gas sample is discussed in published patentapplication US 2010/0027004 (serial no. U.S. patent application Ser.No.12/427,485, filed Apr. 21, 2009), the entirety of which is herebyincorporated by reference herein. While in the present embodiment thereference spectra are stored in the calibration flash RAM 324, inalternative embodiments the reference spectra may instead be partiallyor entirely stored in the firmware flash RAM 328, or in any other typeof suitable memory that is accessible to the DSP 300 while the DSP 300is analyzing the measured absorption spectra.

Following speciation of the gas sample by the DSP 300, the DSP 300transfers speciation results to a microcontroller 302. Like the DSP 300,the microcontroller 302 is connected to the firmware flash RAM 326,which in addition to storing instructions and algorithms for executionby the DSP 300, also stores instructions and algorithms for execution bythe microcontroller 302. Also communicatively coupled to themicrocontroller 302 are heaters 308 for maintaining the temperature ofthe gas analyzer 114 above freezing; a stepper motor 310, the actuationof which controls an optical filter 407 (not present in FIG. 3, butpresent and labelled in FIG. 4) contained within the hydrocarbon sensor202 that controls what wavelength of light is directed through the gassample; sample and bubbler pumps 214, 232 and solenoid valves 218, 220,224, 228 used to control gas flow through the gas analyzer 114, asdiscussed in more detail below; a temperature sensor 316 that measuresthe current temperature within the gas analyzer 114, which providesfeedback to the microcontroller 302 to better operate the heaters 308; apower monitor 318 for monitoring voltage levels within the gas analyzer114 for diagnostic purposes; the carbon dioxide sensor 204; an Ethernetconnection 328 that can be used to interface with the network 118; aserial connection such as a RigComm™ interface that can be used tocommunicate with the data recording device 116; a debug port 332 thatcan be used when troubleshooting the gas analyzer 114; electricallyerasable programmable read only memory (EEPROM) used to storeinfrequently changed data, such as the serial number of the gas analyzer114; and a lifetime monitor 338 that records the duration for which thegas trap 700 is used. As is indicated in FIG. 3, communication betweenthe microcontroller 302 and the DSP 300, the RigComm™ interfaces 334,336, and the carbon dioxide sensor 204 are done via a universalasynchronous receiver/transmitter (UART) embedded within themicrocontroller 302; communication between the microcontroller 302 andthe firmware flash RAM 326, the EEPROM 330, and the debug port 332 isdone using a serial peripheral interface (SPI) bus; and communicationbetween the microcontroller 302 and the lifetime monitor 338 is doneusing an inter-integrated circuit (I²C) bus. The DSP 300 communicateswith the firmware flash RAM 326 and the ADC 306 using a SPI bus.

The microcontroller 302 can configure the gas analyzer 114 to operate inmultiple operating modes: calibration mode, zeroing mode, measurementmode, and two purge modes. In typical operation, the microcontroller 302typically operates the gas analyzer 114 in measurement mode.

Measurement Mode

During measurement mode, the microcontroller 302 configures the pumps214, 232 and solenoid valves 218, 220, 224, 228 to convey the gas samplefrom the gas trap 700 outside of the gas analyzer 114 to the hydrocarbonsensor 202 for analysis and, once analyzed, from the hydrocarbon sensor202 back outside the gas analyzer 114 for discharge to atmosphere. Thegas trap 700 is fluidly coupled to the gas analyzer at a sample inlet203 via a gas sample conduit (not shown) contained within a tubingbundle 210. From the sample inlet 203, the gas sample travels along asample flowline 201 through an open, two-way solenoid valve 218, and toa sample filter 226. The sample filter 226 removes from the gas sampleany solid or liquid contaminants that may be present in the gas sample.An exemplary sample filter 226 is a model 360A filter housing fittedwith a 30CS filter element, both from United Filtration Systems. Afterexiting the sample filter 226, the gas sample continues along the sampleflowline 201 and passes through a three-way tee 222 to a closed,three-way solenoid valve 220. When the valve 220 is in the closed state,the gas sample is conveyed into the hydrocarbon sensor 202 via a gasinlet 402 (not labelled in FIG. 2, but labelled in FIG. 4( a)) in thehydrocarbon sensor 202, where the DSP 300 analyzes the gas sample bycomparing absorption spectra measured by the hydrocarbon sensor 202 toreference absorption spectra stored in the calibration flash RAM 324.

Following analysis, the gas sample exits the hydrocarbon sensor 202through a gas outlet 404 in the hydrocarbon sensor 202 (not labelled inFIG. 2, but labelled in FIG. 4( a)). A needle valve 212 is attached tothe gas outlet 404 that is manually adjustable to control the flow rateof the gas sample as it exits the hydrocarbon sensor 202. After passingthrough the needle valve, the gas sample continues along the sampleflowline 201 through a sample pump 214 and exits the gas analyzer 114through a sample outlet 205. The sample pump 214 pressurizes theentirety of the sample flowline 201 such that the gas sample is forcedthrough the sample flowline 201 from the sample inlet 203 to the sampleoutlet 205.

While in measurement mode, air pressure is used to maintain a certainvolume of drilling fluid in the gas trap 700. This volume of fluid isthen agitated so as to liberate the hydrocarbons that form part of thegas sample that the gas analyzer 114 analyzes. In addition tohydrocarbons, other gases that may be liberated from the drilling fluidinclude carbon dioxide and hydrogen sulphide. The air used to maintainfluid volume in the gas trap 700 is “bubbler air” and is drawn in froman air source, such as the atmosphere, outside the gas analyzer 114through a bubbler inlet 207 along a bubbler flowline 215 by virtue ofpressurization caused by a bubbler pump 232 fluidly coupled along thebubbler flowline 215. The bubbler pump 232 draws the bubbler air alongthe bubbler flowline 215 and through a bubbler filter 234 that removesfrom the bubbler air any solid or liquid contaminants that may bepresent in the bubbler air. An exemplary bubbler filter 234 is a is amodel 360A filter housing fitted with a 30CS filter element, both fromUnited Filtration Systems. After being filtered, the bubbler air ispumped through the bubbler pump 232 and through a closed, three-waysolenoid valve 228. When in the closed position, the bubbler air isdirected out through a needle valve 230 attached to one of the ports ofthe three-way solenoid valve 228 that is adjustable so as to control therate of flow of the bubbler air as it exits the gas analyzer 114 througha bubbler outlet 209. The bubbler outlet 209 is fluidly coupled to abubbler air conduit (not shown) within the tubing bundle 210. Thebubbler air conduit conveys the pressurized bubbler air to the gas trap700, where it is used to prevent the drilling fluid in the gas trap 700from exceeding a certain height, thereby also maintaining a certainvolume of the drilling fluid. Optionally, a heat trace may be present inthe tubing bundle 210 with the gas sample conduit and the bubbler airconduit to prevent the conduit from freezing when used in coldenvironments; the heat trace may be powered using a power supply (notshown) within the gas analyzer 114.

To allow the gas analyzer 114 to more accurately speciate hydrocarbonsin the measurement mode, the gas analyzer 114 is calibrated in thecalibration mode prior to entering the measurement mode.

Calibration Mode

Optionally, to enhance the accuracy of the gas analyzer 114, the gasanalyzer 114 may be calibrated in the calibration mode prior to use inthe measurement mode. In the calibration mode, the microcontroller 302configures the pumps 214, 232 and the solenoid valves 218, 220, 224, 228in the same manner as in the measurement mode. However, when in thecalibration mode, one or more reference gas samples of known compositionare fed to the gas analyzer 114 and speciated. If the gas analyzer 114outputs speciation results that vary by more than a certain calibrationthreshold from the known compositions of the reference gas samples, theDSP 300 computes calibration factors that compensate for the differencebetween the speciation results and the known compositions of thereference gas samples. The calibration factors are stored in thecalibration flash RAM 324 and are subsequently applied by the DSP 300 toadjust speciation results computed during the measurement mode toincrease the accuracy of the readings that the gas analyzer 114 outputs.

Zeroing Mode

From time to time to help ensure speciation accuracy, the gas analyzer114 can be zeroed. I.e., a gas sample having no hydrocarbons can be sentthrough the hydrocarbon sensor 202 and the gas analyzer 114 can be resetaccordingly in order to mitigate any measurement drift that may haveaccrued over time. In the present embodiment, the gas analyzer 114 iszeroed prior to running the calibration mode for the first time, and isalso zeroed from time to time thereafter.

In zeroing mode, the microcontroller 302 actuates the solenoid valve 220such that it is in an opened state; the remainder of the solenoid valves218, 224, 228 are in the same state as described above with respect tothe measurement and calibration modes. When the solenoid valve 220 is inthe opened state, suction generated by the sample pump 214 drawsatmospheric air in from a zeroing air inlet 211; this atmospheric air ishereinafter referred to as “zeroing air”. The zeroing air is suckedthrough a disposable filter unit (DFU) 216, which filters from thezeroing air any hydrocarbons that it may contain. Following filtering,the zeroing air passes through the solenoid valve 220, is analyzed bythe hydrocarbon sensor 202, and then is pumped out of the gas analyzer114 via the sample outlet 205.

Purge Modes

The microcontroller 302 is capable of initiating two types of purging: a“low pressure purge” that removes debris that has collected in thesample filter 226, and a “high pressure purge” that clears debris thathas collected in the sample flowline 201 and that is impeding gas samplecollection and analysis. Both the high pressure and low pressure purgesare typically periodically initiated while the gas analyzer 114 isoperating in measurement mode.

To initiate the low pressure purge, the microcontroller 302 actuates thetwo-way solenoid valve 224 from a closed into an opened position. Whenopen, the solenoid valve 224 fluidly couples a drain 217 of the samplefilter 226 to a discharge outlet 213 through which waste can exit thegas analyzer 114. This allows debris that has collected in the samplefilter 226 to pass through the solenoid valve 224 and to exit the gasanalyzer 114 via the discharge outlet 213. During typical operation, themicrocontroller 302 initiates the low pressure purge periodically whilethe gas analyzer 114 is operating in the measurement mode. For example,the gas analyzer 114 may initiate the low pressure purge once every 120minutes, during which time the solenoid valve 224 is held open for 20 to30 seconds.

To initiate the high pressure purge, the microcontroller 302 uses thebubbler pump 232 to build up pressure within the sample filter 226. Inorder to do this, the microcontroller 302 puts the valves 218 and 224into the closed state, and puts the valves 220 and 228 into the openstate while the bubbler pump 232 is operating. The bubbler pump 232consequently pumps bubbler air from the bubbler inlet 207, through thevalve 228, through the tee 222, and into the sample filter 226, whichacts as a pressure reservoir. Because both of the valves 218 and 224 arein the closed state, pressure builds up within the sample filter 226.After a certain period of time, for example 30 seconds, themicrocontroller 302 opens the valve 218 and a burst of pressurized airis discharged from the sample filter 226 and rushes through the sampleflowline 201 and out of the sample inlet 203, thereby clearing thesample flowline 201.

In contrast to the low pressure purge, the microcontroller 302 does notinitiate the high pressure purge based on time. Instead, themicrocontroller 302 monitors readings generated by a pressure sensor 208that is affixed to the hydrocarbon sensor. The pressure sensor 208measures the pressure that the sample pump 214 must overcome in order tointake air through either of the zeroing air inlet 211 and the sampleair inlet 213. When the pressure required to intake air through eitherof the inlets 211, 213 exceeds a certain threshold, such as around 5kPa, the microcontroller 302 infers that a blockage in the flowlinesattached to the inlets 211, 213 is preventing proper airflow andconsequently initiates the high pressure purge. The high pressure purgecan also be triggered manually by, for example, having an operator ofthe gas analyzer 114 actuate a switch on the data recording device 116that is electrically coupled to the microprocessor 302.

Referring now to FIGS. 4( a) and (b), there are depicted perspective andsectional views, respectively, of the hydrocarbon sensor 202. Located atone end of the sensor 202 are the gas inlet 402 and gas outlet 404through which the gas sample enters and exits the hydrocarbon sensor202, respectively, and which are both located along and fluidly coupledto the sample flowline 201. After entering the hydrocarbon sensor 202,the gas sample enters a U-shaped gas cell 408. The gas sample enters thegas cell 408 at point A in FIG. 4( b) and travels sequentially throughpoints B, C and D prior to exiting the gas cell 408 and the hydrocarbonsensor 202 through the gas outlet 404. While the gas sample is residentin the gas cell 408, an infrared emitter 400 generates infrared light inthe near infrared range, which is directed into the gas cell 408. Theinfrared light travels along one branch of the gas cell 408 from point Bto point A, reflects off of a first reflector 410 and then a secondreflector 412, and travels in an opposite direction along a secondbranch of the gas cell 408 from point D to point C; the distance theinfrared light travels from point B to point A and from point D to pointC is the “path length” of the infrared light; in the depictedembodiment, the distance from point A to point D is not included in the“path length” because the infrared light is not passing through the gassample when travelling from point A to point D. The microcontroller 302actuates the stepper motor 310, which is connected to the optical filter407 located between the infrared emitter 400 and the gas cell 408. Apositional encoder 401 monitors the position of the stepper motor 310and reports the position to the microcontroller 302. Actuation of thestepper motor 310 results in the optical filter 407 allowing only acertain wavelength of the infrared light to pass through the gas sampleat any one time; continued actuation of the stepper motor 310 irradiatesthe gas sample with light over a select range of wavelengths. In thepresent embodiment the wavelengths used are centred on about 1.70 μm andrange from about 1.55 μm to 1.85 μm, although in alternative embodimentsdifferent wavelength ranges can be used. For example, in an alternativeembodiment the wavelengths may be selected from elsewhere within thenear infrared range, which extends from about 0.80 μm to about 2.50 μm.Part of the infrared light is absorbed by the hydrocarbons in the gassample present in the gas cell 408. The light that is not absorbedreflects off a third reflector 414 and is directed into the preamp 206,where the absorbed spectra is converted into analog form and sent to theADC 306 for analysis by the DSP 300 and the microcontroller 302. Whilethe gas sample is being irradiated, the pressure sensor 208 measures thepressure level within the gas cell 202 and the carbon dioxide sensor 204measures the level of carbon dioxide of the gas sample. In the depictedembodiment, the infrared emitter 400 is an incandescent infrared lightsource; in alternative embodiments, however, the light source may be acoherent light source of one or more frequencies. For example, the lightsource may be a tunable laser diode.

Using relatively short wavelengths centred on about 1.70 μm to irradiatethe sample gas is advantageous compared to using relatively longwavelengths centred on about 3.30 μm, for example, because linearity ofabsorption is generally greater at 1.70 μm than at 3.30 μm. “Linearityof absorption” refers to the degree to which absorption of infraredradiation linearly correlates with the concentration of hydrocarbons inthe gas sample. For example, assuming perfectly linear absorption andfor any given path length through the gas sample, when the gas samplehas a 1% concentration of hydrocarbons absorption of the infraredradiation will be exactly one half the absorption when the gas samplehas a 2% concentration of hydrocarbons.

The greater the linearity of absorption, the easier it is to perform atleast some of the calculations that are done during operation of the gasanalyzer 114 in both calibration and measurement modes. For example,during calibration mode the calibration factor that is determined at onehydrocarbon composition is extrapolated to determine calibration factorsat other hydrocarbon compositions; this extrapolation is generally lesscomputationally intensive and consequently easier to perform whenlinearity of absorption is relatively high than when linearity ofabsorption is relatively low, such as when wavelengths centred on about3.30 μm are used. Additionally, when linearity of absorption isrelatively high, extrapolation accuracy can also be increased relativeto when linearity of absorption is relatively low, resulting in moreaccurate calculations being performed during the calibration andmeasurement modes.

However, beneficially, when wavelengths centred on about 3.30 μm areused, total absorption per unit volume of the gas sample is higher thanwhen wavelengths centred on about 1.70 μm are used. Consequently, whenwavelengths centred on about 3.30 μm are used, a shorter path length canbe used when generating measurement data than when using wavelengthscentred on about 1.70 μm, and the smaller the hydrocarbon sensor 202that can be manufactured. In the present embodiment, in order to obtainthe benefits conferred by increased linearity, infrared radiationcentred on about 1.70 μm is used and the hydrocarbon sensor 202 is sizedlarge enough and configured with the first and second reflectors 410,412 such that the path length is long enough for useful measurement datato be generated.

Referring now to FIGS. 5( a) and (b), there are depicted embodiments ofmethods for operating the gas analyzer 114. In FIG. 5( a), operation ofthe gas analyzer 114 begins at block 500; block 500 can correspond, forexample, with activation of the gas analyzer 114. The microcontroller302 then cycles the gas analyzer 114 through the calibration and zeroingmodes, respectively, at blocks 502 and 504. At block 506, themicrocontroller 302 causes the gas analyzer 114 to enter the measurementmode. In the present embodiment, measurement is done on a continuousbasis as gas is continuously pumped through the hydrocarbon sensor 202.In the present embodiment the gas sample is pumped through thehydrocarbon sensor at a rate of about 800 cc/minute, althoughalternative flow rates can also be used. In an alternative embodiment,measurement may be done on a batch basis. I.e., the gas analyzer 114 mayintake one gas sample of a certain volume, analyze it, and expel itprior to taking in another gas sample for analysis.

FIG. 5( b) illustrates how the gas analyzer 114 measures the gas sample.At block 510, the gas sample is drawn in through the sample inlet 203and pumped along the sample flowline 201 until it reaches thehydrocarbon sensor 202. Once at the hydrocarbon sensor 202, themicrocontroller 302 activates the infrared emitter 400, which emitsinfrared light that is filtered by the optical filter 407. As thepassband of the optical filter 407 is being continuously adjusted by therotating stepper motor 310, the gas sample is irradiated over a range ofinfrared light (block 512). At block 514, the measured absorptionspectra detected and amplified by the preamp 206 are transmitted to theDSP 300, which compares the measured absorption spectra to the referenceabsorption spectra stored in the calibration flash RAM 324. The degreeof correlation between the two spectra determines how many of each ofmethane, ethane, butane and propane is present in the gas sample. Howmuch of each hydrocarbon is then sent to the microcontroller 302, whichcan output the analysis results over an Ethernet or serial connection tothe data recording device 116. Optionally, the microcontroller 302 mayalso compute and out various ratios potentially useful for geologists.The microcontroller 302 may, for example, compute any one or more of thebalance ratio ([(C1+C2)/(C3+C4+C5)]), the wetness ratio([(C2+C3+C4+C5)/(C1+C2+C3+C4+C5)]*100), the character ratio([(C4+C5)/C3]), or compute the ratio of light hydrocarbons to totalhydrocarbons (the sum of light and heavy hydrocarbons).

Beneficially, the gas analyzer 114 is able to speciate the hydrocarbonsin the gas sample continuously and in real time, which allows the gasanalyzer 114 to output speciation results quickly. Also beneficially,the gas analyzer 114 does not require carrier air to dilute the gassample prior to measurement or to otherwise facilitate speciation, whichsimplifies construction of the gas analyzer 114. I.e., the gas analyzer114 does not mix carrier air with the gas sample to reduce theconcentration of the hydrocarbons in the gas sample to a level such thatthe hydrocarbon sensor 202 can analyze them; instead, the hydrocarbonsensor 202 is able to directly analyze whatever concentration ofhydrocarbons is present in the gas sample directly as liberated from thedrilling fluid. Any air that mixes with the gas sample occurs inrelatively minimal volumes and does so incidentally as a result thesuction that draws the gas sample into the gas analyzer 114 from the gastrap 700. This contrasts with some conventional systems used to speciatehydrocarbons, such as gas chromatographs, which intentionally introducerelatively large volumes of carrier air to a gas sample in order tofacilitate speciation.

Gas Trap

As discussed above, the gas analyzer 114 obtains the gas sample from thegas trap 700. Known gas traps typically use either an air motor that ispowered using pressurized rig air or an AC induction motor in order toagitate the drilling fluid. Each of these motors has drawbacks. Forexample, merely operating the air motor does not inherently generatefeedback that allows the motor operator to know the motor's speed.Instead, in order to measure the speed of the air motor sensors aretypically installed and monitored. Additionally, air motors utilizevoltage to pressure converters that can be difficult to preciselycontrol, which accordingly can make it difficult to precisely controlthe speed of the air motor. Furthermore, on a drilling rig the air motoris fluidly coupled to an air compressor that powers any pneumatics onthe rig; the air provided by this air compressor is called “rig air”.Depending on the number of devices powered using rig air, obtainingsufficient air pressure from the air compressor in order to run the airmotor can be a problem. Another problem related to air motors is that inorder to prevent the rig air from freezing, contaminants such as one orboth of alcohol and antifreeze may be added to the rig air; othercontaminants, such as solid particulates, may also be in the rig air.These contaminants can lead to problems such as corrosion thateventually wreck the air motor.

One drawback of the AC induction motor is its relative inefficiency,which results in its generating a significant amount of waste heatduring operation. Consequently, a cooling fan is typically used inconjunction with the AC induction motor, which can be problematic on adrilling rig on which drilling fluid is splashing and interfering withthe cooling fan's operation. Additionally, the rate of rotation of theAC induction motor varies with the frequency of the electrical signalthat drives the motor. This can result in the speed of the AC inductionmotor varying with its location of use, as some countries transmit ACpower at 50 Hz while others transmit power at 60 Hz. Furthermore, it canbe difficult to obtain speed feedback from the AC induction motor; themotor is consequently often run as part of an open loop system in whichthe motor is simply, and sometimes incorrectly, presumed to be operatingat a certain speed regardless of its actual performance. AC inductionmotors that are used in gas traps are also typically relatively heavy,commonly weighing about 30 lbs.

Additionally, it is beneficial to make the footprint of the gas traprelatively small. After the drilling fluid is pumped from the well, itis deposited into a shaker box. The shaker box acts as a reservoir thatstores the drilling fluid prior to and while the drilling fluid is beingagitated within the gas trap. The gas trap is immersed in the drillingfluid that is in the shaker box and liberates entrained gases from thedrilling fluid in order to generate the gas sample that the gas analyzer114 analyzes. Because shaker boxes are constrained in size, making thefootprint of the gas trap relatively small increases the range of shakerboxes with which the gas trap can be used.

The embodiments of the gas trap 700 depicted in FIGS. 7 through 12utilize a configuration that facilitates the gas trap 700 having arelatively small footprint, and that utilizes a brushless DC motor inlieu of an AC induction motor or an air motor. Doing so helps toameliorate the problems associated with using air motors or AC inductionmotors, and facilitates mounting of the gas trap 700 on to shaker boxesof various sizes.

Referring now to FIGS. 7 to 12, there is depicted a gas trap 700according to a first embodiment. FIG. 7 is a perspective view of the gastrap 700; FIG. 8 is a front elevation view of the gas trap 700; and FIG.9 is a sectional view of the gas trap 700 along line 9-9 of FIG. 7; FIG.10 is a bottom plan view of the gas trap 700; FIG. 11 is a top plan viewof the gas trap 700; and FIG. 12 is a rear elevation view of the gastrap 700. The gas trap 700 includes two adjacent enclosures: a sampleenclosure 702 and a bubbler enclosure 704. At the bottom of the sampleenclosure 702 is a lid 728 that is secured to the sample enclosure 702via a pair of latches 718. Disposed in the lid 728 is a liquid inlet 904(visible in FIGS. 9 and 10) through which drilling fluid may enter thesample enclosure 702. At the top of the sample enclosure 702 is abrushless, DC motor 706 that powers an agitator (visible in FIGS. 9 and10) used to agitate the drilling fluid. Located on top of the DC motor706 is a motor cover 717. The DC motor 706 is secured to the sampleenclosure 702 via a series of bolts 716 that secure the motor cover 717to a flange 720 extending along the periphery of the top of the sampleenclosure 702, thereby clamping the DC motor 706 to the sample enclosure702. A handle 726 is bolted to the motor cover 717 to facilitatecarrying of the gas trap 700. An explosion proof seal 730 is screwedinto the motor cover 717 through which electrical connections (notshown) to the DC motor 706 can be made. A mounting tube 1000 (visible inFIG. 10) can be used to mount the gas trap 700 to the shaker box (notshown).

Adjacent to the sample enclosure 702 is the bubbler enclosure 704. Atthe bottom of the bubbler enclosure 704 is a bubbler air outlet 724, andat the top of the bubbler enclosure 704 is a bubbler enclosure cover722. Extending from the top of the bubbler enclosure cover 722 is thetubing bundle 210 inside of which is the gas sample conduit 710, bubblerair conduit 712, and heat trace 714. The gas sample conduit 710 isfluidly coupled to the sample inlet 203 of the gas analyzer 114 and thebubbler air conduit 712 is fluidly coupled to the bubbler outlet 209 ofthe gas analyzer 114. During operation of the gas trap 700, the bubblerair conduit 712 is fluidly coupled to a bubbler air inlet in the form ofa bubbler air port 918 that fluidly couples two sides of a bubblerenclosure baffle 922. Similarly, the sample air conduit 710 is fluidlycoupled to a gas sample port 920 that fluidly couples the sample airconduit 710 to the interior of the sample enclosure 702.

Referring now to FIG. 9, the sample enclosure 702 is delineated by asample enclosure wall that includes a sample enclosure wall portion 912and a shared wall portion 914, while the bubbler enclosure 704 isdesalinated by a bubbler enclosure wall that includes a bubblerenclosure wall portion 916 and the shared wall portion 914. In thedepicted embodiment, the shared wall portion 914 delineates a portion ofboth the sample enclosure 702 and the bubbler enclosure 704; the sampleenclosure wall portion 912 delineates the remainder of the sampleenclosure 702 but not the bubbler enclosure 704; and the bubblerenclosure wall portion 916 delineates the remainder of the bubblerenclosure 704 but not the sample enclosure 702. Disposed along theshared wall portion 914 are two ports: a liquid port 908 that allowsagitated drilling fluid to enter the bubbler enclosure 704 from thesample enclosure 702, and a gas port 910 that allows the bubbler air toenter the sample enclosure 702 from the bubbler enclosure 704. Asdiscussed in more detail below, the presence of these two ports 908, 910helps to keep the footprint of the gas trap 700 relatively small, whileusing bubbler air to maintain a constant drilling fluid level within thesample enclosure 702. Although in the present embodiment the sampleenclosure 702 and the bubbler enclosure 704 are both cylindrical, inalternative embodiments they may be differently shaped. For example, thesample and bubbler enclosures 702, 704 may be polygonal (regular orirregular) in shape.

The agitator extends axially along the sample enclosure 702 and includesa shaft 900 that has disposed at one end a mixing portion 902. Themixing portion 902 is composed of a triangular mounting plate throughthe corners of which extend three bolts that help to displace andagitate the drilling fluid. The other end of the shaft 900 is insertedinto a rotor 928 of the DC motor 706. The rotor 928 rotates relative toa stator 930, and both the rotor 928 and stator 930 rest on a shoulder926 that is supported by the flange 720 on top of the sample enclosure702. In the embodiment of FIG. 9, the DC motor 706 is frameless and therotor 928 is directly coupled to the shaft 900 using an adhesive such asa retaining compound; in terms of reliability and integrity, directlycoupling the shaft 900 to the rotor 928 is advantageous compared tousing a typically designed, pre-assembled off-the-shelf motor in whichthe motor has an output shaft to which the shaft 900 is then coupled.One pair of bearings 932 a is located above the rotor 928 and anotherpair of bearings 932 b is located below the rotor 928. As the shaft 900is threaded through the rotor 928, the surface of the shaft contacts thebearings 932 a,b, which helps the shaft 900 to spin. Beneficially,because the DC motor 706 is frameless, the bearings 932 a,b can be sizedduring assembly of the DC motor 706 in accordance with the length of theshaft 900, and the shaft 900 can be directly coupled to the rotor 928 asis done using the adhesive in the depicted exemplary embodiment. Byassembling the DC motor 706 in this way, the bearings 932 a,b can beselected to be sufficiently large such that they can withstand theforces applied to them by virtue of typical lateral or bending forcesthat are applied to the shaft 900 during its rotation. In order to keepthe bearings 932 a,b dry and operational, they are beneficially kept arelatively long distance from the drilling fluid, which dictates thatthe shaft 900 be relatively long relative to the spacing between thepairs of bearings 932 a,b. In the present example embodiment, thedistance from the bottom pair of bearings 932 b to the bottom of themixing portion 902 of the shaft 900 (the “overhung load”) isapproximately 13.25 inches, while the spacing between the pairs ofbearings 932 a,b is approximately 2.5 inches. Since the distance ratioof the length of the overhung load to the spacing between the bearings932 a,b is over five, the bearings 932 a,b are subject to moment loadingthat is relatively heavy and greater than a typically designed,pre-assembled off-the-shelf motor having the minimum power ratingsuitable for use in the depicted gas trap 700 is designed to withstand.One potential solution to this problem is to install an additional setof bearings along the interior surface of the sample enclosure 702 toreinforce the shaft 900; however, this is impractical given thatsplashing drilling fluid within the sample enclosure 702 would quicklyclog these bearings. Another potential solution is to use anoff-the-shelf, pre-assembled DC motor that has a higher power rating,and therefore larger bearings, than is required for the gas trap 700;however, this solution wastes power and is therefore relativelyinefficient. Using a DC motor with a higher power rating also means thata motor that is heavier than necessary is used. By using the frameless,DC motor 706 and sizing the bearings 932 a,b during assembly as opposedto using an off-the-shelf DC motor, a relatively efficient and practicalsolution to the problem of withstanding the forces that result fromusing the relatively long shaft 900 results. In the depicted exampleembodiment, each of each of the top pair of bearings 932 a hasdimensions of approximately 20 mm×42 mm×12 mm, and each of the bottompair of bearings 932 b has dimensions of approximately 25 mm×42 mm×9 mm.In the present example embodiment, the DC motor 706 can run at 250 watts(⅓ hp) maximum continuous power.

In the embodiment of FIG. 9, the shoulders 926 taper to form apassageway 934 that leads from the DC motor 706 to the sample enclosure702. At the bottom of this passageway 934 is a sealing portion formedfrom a first sealing element in the form of a lip seal 936 and a secondsealing element in the form of two seals 938 a,b located between the lipseal 926 and the DC motor 706. A small gap is present between the shaft900 and the sealing portion to act as a flame path so as to preventcombustible gases outside of the DC motor 706 from igniting in the eventthat an explosion occurs within the DC motor 706. In the presentembodiment, the gas trap 700 is machined such that the width of the gapis between 0.002 of an inch and 0.006 of an inch; in alternativeembodiments, the width of the gap may differ. The sealing portion fitsclosely around the shaft 900 so as to prevent agitated drilling fluidfrom splashing up into the DC motor 706. Specifically, the lip seal 936is particularly designed to prevent solid particulates from entering theDC motor 706, while the two seals 938 a,b are designed to prevent liquidfrom entering the DC motor 706. In the present embodiment the lip seal936 is made from Buna-N rubber and the two seals 938 a,b are made fromgraphite filled PTFE (Teflon), but in alternative embodiments the seals936, 938 a,b may be made from different materials. At a point ofrelatively high loading immediately below the bottom pair of bearings932 b, the shaft 900 has a diameter of approximately 0.975 inches; at apoint of relatively low loading just below the flame path, the shaft 900has a diameter of approximately 0.7 inches.

A baffle 924 located below the shoulders 926 with an opening to allowthe shaft 900 to pass through also helps to prevent splashing drillingfluid from plugging the gas sample port 920. A polyurethane disc 940placed on the shaft 900 and aligned with, and located slightly below,the opening in the baffle 924 also helps to prevent splashing drillingfluid from entering the inside of the DC motor 706.

The gas trap 700 is configured to be able to use the bubbler air tomaintain a certain height of the drilling fluid when the drilling fluidis greater than the marker labelled L1 in FIG. 9. L1 corresponds to thelocation of the bubbler air outlet 724. During normal operation, thepressures of the sample enclosure 702 and the bubbler enclosure 704 areequalized by virtue of air being able to pass freely through the gasport 910. Consequently, when the bubbler air is sufficientlypressurized, the bubbler air forces the drilling fluid in both thesample and bubbler enclosures 702, 704 down to L1 prior to exiting thebubbler enclosure 704 through the bubbler air outlet 724. In the presentexemplary embodiment, the bubbler air is pressurized to approximately0.5 psi; in alternative embodiments the bubbler air may be pressurizedto a different level depending on, for example, the density of thedrilling fluid and the dimensions of the gas trap 700.

When no bubbler air is being injected into the gas trap 700, the gastrap 700 is beneficially immersed no deeper than the marker labelled L2in FIG. 9, which corresponds to the location of the gas port 910. Thisis because the when there is no bubbler air, the drilling fluid willrise to level L2. Keeping the drilling fluid lower than L2 reduces thelikelihood that the drilling fluid will plug any or all of the gas port910, the bubbler air port 918, and the gas sample port 920 which couldprejudice operation of the gas trap 700.

In order to liberate gases that are entrained in the drilling fluid, theDC motor 706 rotates the agitator, which consequently agitates thedrilling fluid. Agitation of the drilling fluid consequently results inthe gas sample being released into the sample enclosure 702. The samplepump 214 in the gas analyzer 114 sucks the sample gas from the sampleenclosure 702, through the gas sample port 920 and the gas sampleconduit 710, and into the gas analyzer 114 via the sample inlet 203 foranalysis as described above. While the drilling fluid is being agitated,the bubbler pump 232 outputs pressurized bubbler air out through thebubbler outlet 209, the bubbler air conduit 712, the bubbler air port918, and into the sample enclosure 702 and the bubbler enclosure 704 soas to maintain the level of drilling fluid within the sample enclosure702 substantially constant at level L1 . Beneficially, as the bubblerpump 232 is dedicated to providing the bubbler air, problems associatedwith pressure variations in rig air are avoided. Furthermore, as theheat trace 714 can be operated to prevent the bubbler air from freezing,contaminants such as alcohol and antifreeze do not need to be added tothe bubbler air. Additionally, because of the heat trace 714, moisturedoes not need to be removed from the gas sample using a desiccant toprevent freezing as may be done in conventional systems.

After the gas sample is liberated from the drilling fluid, the agitateddrilling fluid exits the sample enclosure 702 and enters the bubblerenclosure 704 via the liquid port 908. Because the drilling fluiddirectly enters the bubbler enclosure 704 from the sample enclosure 702,no external baffles or containers need to be placed outside of thesample or bubbler enclosures 702, 704 to prevent splashing or tootherwise direct the drilling fluid after it leaves the gas trap 700.Instead, the drilling fluid exits the gas trap 700 by being forced outthrough the bubbler air outlet 724 at the bottom of the bubblerenclosure 704, which substantially mitigates any problems related tosplashing.

In the present embodiment the liquid port 908 is used primarily to allowthe agitated drilling fluid to exit the sample enclosure 702 and toenter the bubbler enclosure 704, and the gas port 910 is used primarilyto allow gases to be exchanged between the sample and bubbler enclosures702, 704 so as to equalize pressure between the two enclosures 702, 704.However, gases may pass through the liquid port 908 and the liquid port908 may therefore also contribute to equalizing pressures between theenclosures 702, 704. Similarly, depending on the height of the drillingfluid, some of the agitated drilling fluid may enter the bubblerenclosure 704 from the sample enclosure 702 via the gas port 910. Inalternative embodiments (not depicted), a single fluid port may be usedto both allow drilling fluid to enter the bubbler enclosure 704 from thesample enclosure 702 and to equalize pressure between the two enclosures702, 704; multiple fluid ports may be used to both allow drilling fluidto enter the bubbler enclosure 704 from the sample enclosure 702 and toequalize pressure between the two enclosures 702, 704; or a combinationof any of fluid ports that operate to both allow drilling fluid to enterthe bubbler enclosure 704 from the sample enclosure 702 and to equalizepressure between the two enclosures 702, 704, liquid ports 908 thatoperate primarily to allow the agitated drilling fluid to exit thesample enclosure 702 and to enter the bubbler enclosure 704, and gasports 910 that operate primarily to allow gases to be exchanged betweenthe sample and bubbler enclosures 702, 704 so as to equalize pressurebetween the two enclosures 702, 704 may be used.

Beneficially over an AC induction motor, the DC motor 706 generatessignificantly less waste heat (the DC motor 706 can be 80-85% efficient,while an AC induction motor is typically around 50% efficient) and isoperable at a user-controllable rate independent of the frequency of theAC electricity used to power the motor. Additionally, the controller(not shown) used with the DC motor 706 is able to inherently measure theoperating speed and the torque generated by the DC motor 706, which arerespectively directly proportional to the degree to which the drillingfluid is being agitated and how much work the DC motor 706 isperforming. With an AC induction motor, such measurements are typicallyobtained not through any kind of motor controller, but through a morecomplex arrangement of sensors mounted to or near the motor, or suchmeasurements are not used at all and the AC induction motor is run in anopen loop configuration. Furthermore, beneficially compared to an airmotor, the DC motor 706 is operable independently of the current airpressure available through the rig air and is not contaminated by anycontaminants present in the rig air. The DC motor 706 is alsosignificantly lighter than a typical AC induction motor; the DC motor706 can weigh approximately three to four pounds, while a typical ACinduction motor can weigh roughly an order of magnitude more, or about30 pounds.

In the depicted embodiment, the gas trap 700 is shown as using the DCmotor 706 to power agitation and the liquid port 908 to dischargeagitated drilling fluid from the sample enclosure 902 to the bubblerenclosure 904. However, in alternative embodiments (not shown) the gastrap 700 may use the DC motor 706 without discharging agitated drillingfluid into the bubbler enclosure 904, or the gas trap 700 may dischargeagitated drilling fluid into the bubbler enclosure 904 via the liquidport 908 without incorporating the DC motor 706. For example, accordingto one alternative embodiment (not shown), the gas trap shown in U.S.Pat. No. 6,666,099 may be modified to be powered using the DC motor 706.

Furthermore, in the depicted embodiment, the gas trap may be made from amaterial such as stainless steel. In alternative embodiments, anysuitable material can be used, such as a corrosion resistant alloy or amaterial that is not corrosion resistant so long as appropriatecorrosion allowances are considered. Furthermore, in the depictedembodiment the sample enclosure 702 and the bubbler enclosure 704 sharethe shared wall portion 914. In an alternative embodiment (notdepicted), there does not need to be any shared wall portion between thesample and bubbler enclosures 702, 704. For example, the sample andbubbler enclosures 702, 704 may both be cylindrical in shape andseparate from each other, but there may be a fluid conduit such astubing that fluidly couples the sample and bubbler enclosures 702, 704together.

The fluid conduit may optionally be slanted downwards from the sampleenclosure 702 towards the bubbler enclosure 704 so as to facilitateemptying of drilling fluid into the bubbler enclosure 704.

Any of the foregoing methods may be encoded on a computer readablemedium for execution by a processor such as the microprocessor 302, theDSP 300, a programmable logic controller, a field programmable gatearray, a controller, and an application specific integrated circuit. Thecomputer readable medium may be, for example, the SDRAM 322, thecalibration flash RAM 324, the firmware flash RAM 326, disc-based mediasuch as DVD-ROMs, read only memories such as EEPROMs, any suitablemagnetic storage media such as hard drives, and any other suitable typeof storage medium.

For the sake of convenience, the embodiments above are described asvarious interconnected functional blocks or distinct software modules.This is not necessary, however, and there may be cases where thesefunctional blocks or modules are equivalently aggregated into a singlelogic device, program or operation with unclear boundaries. In anyevent, the functional blocks and software modules or features of theflexible interface can be implemented by themselves, or in combinationwith other operations in either hardware or software.

While particular embodiments have been described in the foregoing, it isto be understood that other embodiments are possible and are intended tobe included herein. It will be clear to any person skilled in the artthat modifications of and adjustments to the foregoing embodiments, notshown, are possible.

1. A method for analyzing a gas sample conveyed in a drilling fluid, themethod comprising: (a) liberating the gas sample from the drillingfluid, wherein the gas sample comprises one or more of methane, ethane,propane, and butane; (b) irradiating the gas sample with infraredradiation spanning a wavelength range comprising near-infraredwavelengths; (c) simultaneously detecting absorption spectra associatedwith irradiating each of the one or more of methane, ethane, propane,and butane; and (d) determining a composition of the gas sample from theabsorption spectra, the composition comprising a concentration of anyone or more of the methane, ethane, propane and butane.
 2. A method asclaimed in claim 1 wherein the wavelength range is from about 1.55 μm toabout 1.85 μm.
 3. A method as claimed in claim 1 further comprising fromthe absorption spectra, determining how much pentane is present in thegas sample.
 4. A method as claimed in claim 1 further comprisingdetermining how much carbon dioxide is present in the gas sample.
 5. Amethod as claimed in claim 1 wherein the butane comprises one or both ofi-butane and n-butane.
 6. A method as claimed in claim 1 whereindetermining the composition of the gas sample comprises determining theconcentrations of any two or more of the methane, ethane, propane andbutane.
 7. A method as claimed in claim 6 wherein determining thecomposition of the gas sample comprises determining the concentrationsof any three or more of the methane, ethane, propane and butane.
 8. Amethod as claimed in claim 7 wherein determining the composition of thegas sample comprises determining the concentrations of each of themethane, ethane, propane and butane.
 9. A method as claimed in claim 1wherein a tunable laser diode emits the infrared radiation.
 10. A methodas claimed in claim 1 wherein liberating the gas sample from thedrilling fluid is performed using a gas trap, and further comprisingpumping air from an air source into the gas trap to maintain thedrilling fluid at a certain height within the gas trap.
 11. A method asclaimed in claim 10 further comprising heating the gas sample after itis liberated from the drilling fluid and heating the air from the airsource prior to pumping the air into the gas trap.
 12. A method asclaimed in claim 10 further comprising: (a) pressurizing, in a pressurereservoir, air from the air source; and (b) discharging pressurized airfrom the pressure reservoir into a flowline used to intake the gassample from the gas trap to clear the flowline.
 13. An apparatus foranalyzing a gas sample extracted from a drilling fluid, the apparatuscomprising: (a) an sample inlet configured to receive the gas sample,wherein the gas sample comprises one or more of methane, ethane,propane, and butane; (b) a hydrocarbon sensor comprising a gas cellfluidly coupled to the sample inlet and configured to contain a portionof the gas sample; (c) an infrared emitter positioned to irradiate thegas cell with infrared radiation spanning a wavelength range comprisingnear-infrared wavelengths; (d) a detector aligned with a path of theinfrared radiation to simultaneously detect absorption spectraassociated with irradiating each of the one or more of methane, ethane,propane, and butane within the gas cell; (e) a sample outlet fluidlycoupled to the gas cell and configured to discharge the gas sample; and(f) a processor communicatively coupled to the detector and to a memory,the memory having statements and instructions encoded thereon toconfigure the processor to determine a composition of the gas samplefrom the absorption spectra, the composition comprising a concentrationof any one or more of the methane, ethane, propane and butane.
 14. Anapparatus as claimed in claim 13 wherein the wavelength range is fromabout 1.55 μm to about 1.85 μm.
 15. An apparatus as claimed in claim 13wherein the statements and instructions encoded on the memory furtherconfigure the processor to determine how much pentane is present in thegas sample.
 16. An apparatus as claimed in claim 13 further comprising acarbon dioxide detector fluidly coupled to the gas cell, and wherein thestatements and instructions encoded on the memory further configure theprocessor to determine how much carbon dioxide is present in the gassample.
 17. An apparatus as claimed in claim 13 wherein the statementsand instructions encoded on the memory further configure the processorto determine how much of one or both of n-butane and i-butane arepresent in the gas sample.
 18. An apparatus as claimed in claim 13wherein the statements and instructions encoded on the memory configurethe processor to determine the concentrations of any two or more of themethane, ethane, propane and butane.
 19. An apparatus as claimed in anyclaim 18 wherein the statements and instructions encoded on the memoryconfigure the processor to determine the concentrations of any three ormore of the methane, ethane, propane and butane.
 20. An apparatus asclaimed in claim 19 wherein the statements and instructions encoded onthe memory configure the processor to determine the concentrations ofeach of the methane, ethane, propane and butane.
 21. An apparatus asclaimed in claim 13 wherein the infrared emitter is a tunable laserdiode.
 22. An apparatus as claimed in claim 13 further comprising abubbler pump, a bubbler inlet and a bubbler outlet, wherein the bubblerpump is fluidly coupled to the bubbler outlet and to an air source viathe bubbler inlet and is configured to pump bubbler air out through thebubbler outlet.
 23. An apparatus as claimed in claim 22 furthercomprising a gas trap configured to liberate the gas sample from thedrilling fluid, and having a bubbler air port fluidly coupled to thebubbler pump via a bubbler air conduit and a gas sample port fluidlycoupled to the sample inlet via a gas sample conduit, wherein thebubbler air pumped from the bubbler pump through the bubbler air conduitand into the bubbler air port maintains the drilling fluid at a certainheight within the gas trap and wherein the gas sample is dischargedthrough the gas sample port and gas sample conduit to the sample inlet.24. An apparatus as claimed in claim 22 further comprising a tubingbundle surrounding the bubbler air and gas sample conduits, the tubingbundle comprising a heat trace configured to heat the bubbler air andgas sample conduits.
 25. An apparatus as claimed in claim 22 furthercomprising: (a) a sample filter; (b) valving configurable inmeasurement, pressurizing and purging states, the valving fluidlycoupling the sample inlet to the hydrocarbon sensor through the samplefilter when in the measurement state, fluidly coupling the bubbler pumpto the sample filter such that pressure builds within the sample filterwhen in the pressurizing state, and fluidly coupling the bubbler pump tothe sample inlet through the sample filter when in the purging statesuch that pressurized air within the sample filter is discharged throughthe sample inlet.
 26. A computer readable medium having encoded thereonstatements and instructions configured to cause a processor to execute amethod as claimed claim 1.